This invention relates to the production of die cast rotors for electric motors and which uses a vertical die cast press and metal heating and transfer apparatus or system as disclosed in U.S. Pat. No. 5,332,026 which issued to the assignee of the present invention and the disclosure of which is herein incorporated by reference. As disclosed in the patent, an electric motor rotor includes a stack of metal laminations mounted on a cylindrical arbor, and the laminations have peripherally spaced slots which extend between an annular cavity within an upper mold member and an annular cavity within a lower mold member. Molten copper material is poured into a shot cavity or chamber of the press, and the molten material is forced upwardly by the shot piston through sprue passages within the lower mold member. The molten material fills the lower cavity to form one endring for the rotor, and the molten material continues to flow upwardly through the slots in the laminations and into the upper cavity to form the opposite endring and copper bars which integrally connect the upper and lower endrings.
It has been found that if the molten copper material is not precisely prepared and/or is not at the proper temperature, the cast bars within the laminations and connecting the endrings may have defects, such as porosity, which reduces the performance of the rotor. If the defects in the cast copper bars and endrings are significant, the rotor must be scrapped, which significantly increases the production costs for the rotors which are acceptable.
Motor rotors have been constructed with the use of extruded copper bars inserted into the peripheral spaced slots or openings within the laminations, and preformed endrings have been brazed to the projecting end portions of the copper bars, for example, as disclosed in U.S. Pat. Nos. 5,398,404 and 6,345,433. Rotor endrings have also been formed by spraying molten copper plasma into cavities formed around the end portions of the bars projecting from the rotor laminations, for example, as disclosed in U.S. Pat. No. 5,185,918. Other various methods of joining preformed endrings to projecting end portions of the bars are disclosed in U.S. Pat. Nos. 4,131,990, 6,088,906 and 6,877,210.